This application is a 371 of PCT/SE 98/01659, filed Sep. 16, 1998.
The present invention relates to a load-bearing vehicle structure of composite material, and a method for moulding such a load-bearing vehicle structure.
The invention concerns the fields of fibre-reinforced thermoplastic composites, sandwich structures, and compression moulding.
The present invention is applicable within the field of vehicle components with low weight and high stiffness and load-bearing capability, for example in floor structures of motor vehicles.
Previously, as a rule, conventional load-bearing vehicle structures, such as for example floor structures in motor vehicles, have been manufactured from different sheet metal constructions.
The increasing demands for vehicles with low weight, aimed at reducing fuel consumption, has resulted in an increased use of different thermosetting plastic composites in load-bearing vehicle structures.
An example of such thermosetting plastic composites is glass fibre reinforced vinyl ester plastic. When manufacturing components of this type, reinforcement material is preformed for example in the form of glass fibre mats and is placed in a collapsible moulding tool in order to be impregnated with thermosetting matrix material therein. When the curing has proceeded far enough, the moulding tool is opened and a component of reinforced thermosetting plastic is removed.
A disadvantage which may be perceived with thermosetting plastic composites is the comparatively long curing time which is necessary when moulding components of thermosetting plastic. Furthermore, in certain cases, it might be difficult to obtain a uniform impregnation of the reinforcement material with matrix material.
Accordingly, the first object of the present invention is to provide a load-bearing vehicle structure of composite material which eliminates the problems which may be perceived with the thermosetting plastic composites which have previously been utilized in load-bearing vehicle structures for the purpose of reducing the weight of a motor vehicle.
In accordance with claim 1, this first object is achieved by means of the load-bearing vehicle structure according to the invention comprising first and second surface materials with reinforcement fibres, and one or several intermediate pieces of core material which are arranged in a pattern adapted to a load-bearing material structure, and that the surface material and/or the core material thereby comprise(s) thermoplastic material, and that the first surface material is attached by means of thermal bonds to first faces of the piece or pieces of core material and that the second surface material is attached by means of thermal bonds to second, opposing faces of the piece or pieces of core material.
Furthermore, a second object of the present invention is to provide a simple and rapid method for moulding such a load-bearing vehicle structure.
In accordance with claim 9, this second object is achieved by means of the method according to the invention comprising preforming and arranging first and second surface materials and one or several pieces of core material in a pattern which is adapted to a load-bearing material structure in order to provide a material batch, and moulding the material batch using a moulding tool, and that the material batch thereby comprises thermoplastic material which is heated to a temperature above the softening temperature and that the heated material batch is placed between mould parts of the moulding tool in an opened position, whereafter the mould parts are pressed together around the material batch in order to achieve forming and cooling of said material batch to a temperature below said softening temperature, and that the mould parts thereafter are opened and a blank is removed from the moulding tool in order to, after trimming and/or making of holes, provide a load-bearing vehicle structure.